The invention concerns a technique for measuring small changes in the thickness profile of band-shaped materials, i.e., materials such as paper which are produced in a continuous web. The invention relates particularly to measuring small changes in the thickness profile of photographic base papers. A method and apparatus is described here for measuring relatively small changes in the thickness profile of band-shaped or web material in a coiled or wound condition. The device includes a measuring sensor with a scanning tip which is supported in a movable manner by a block and casing and which are moved in an axial direction over the surface of a reel of the material. The measuring sensor is positioned in the center of the rectangular block. The dimension of the block thereby preferably adds a multiple factor to the change of thickness profile to be determined.
During the production and processing of band-shaped or web material, for example, during the rolling of photographic paper material, tensions arise through the movement of material between the rollers, or roller frames, or a winch, or the like. This tension can lead to a deformation of the band-shaped or web material. The tension must be measured in order for a consistent traction to be maintained on the band material.
One known technique involves positioning a conventional tension measuring device between two roller frames or between one roller frame and a winch. Such a tension measuring device might abut the band-shaped or web paper and respond to a pressure exerted against the moving web. One such tension measuring device might be positioned on each side of the band or web during rolling. Additional devices may differentially compute and indicate the response of the tension measuring devices so as to monitor the distribution of tension over the width of the band or web. Such devices are disclosed for example in DE-PS No. 678 021.
A further known technique allows band-shaped or web materials to run over a series of rollers in relation to the thickness profile. The measuring rollers are biased for elastic, resilient movement. Additional rollers that support the springs or bias means are positioned between the measuring rollers. The measuring rollers change position in response to changes of the thickness profile of the band-shaped or web material since they remain in contact with the surface of the material. The measuring rollers produce electrical control signals in relation to such changes in position.
As taught by DD-PS No. 28 194, a further known technique positions a number of rollers in a floating manner on a common axis. The rollers maintain contact with the band or web material and scan the material at least at three points. The rollers change position as the thickness profile of the material changes. Changes in roller position create electrical voltage signals. The electrical signals can be used via a feedback control circuit to alter adjustment of the rollers.
The known techniques are expensive and relatively limited in sensitivity to thickness measurement. They can measure and control thickness of the band-shaped or web material only to the same manufacturing tolerance as that embodied in the measuring tool, e.g., the roller frame. These known techniques do not have the ability to mechanically amplify the physical movement of the measuring tool in relation to the physical deformity, or variation, in thickness of the band or web material.
It is furthermore known (DE-OS No. 32 31 965) to measure the thickness profile of band-shaped or web material with a device which includes a square-shaped measuring head with a boring with a measuring sensor which is supported in a springing elastic manner upwardly and downwardly, which produces electrical signals, so that the measuring head and the measuring sensor are in contact with the surface to be measured. By means of such a device, it should be possible to measure, for example, thickness differences of a coated paper tape, which can be detected as a bulge, if the paper band is rolled up on the roller. In the case of paper, this involves, for example, a photographic base paper, which is coated with polyethylene. In practice, however, it has been shown that this device works very imprecisely and does not permit reliable measuring results which could permit conclusions regarding specific thickness changes, particularly not if these changes in thickness are small and if the roller varies greatly in its consistency.